The utilization of variable transmissions for adjusting shaft speed and/or torque multiplication has been the subject of numerous investigations and correspondingly numerous transmission designs. Such torque multiplying speed varying transmissions have general applicability as industrial drives for use in such applications as pump drives, conveyor drives and the like. Of course, vehicular applications are the most well known and perhaps the most challenging.
Prior art variable speed transmissions take a great variety of forms. Most such transmissions are not truly mechanical variable speed transmissions but rather depend on the intervention of other media. For example, the conventional present day automatic transmission is in fact a hydraulic torque convertor that incorporates a mechanical shifting mechanism for selecting gear ratios; thus, a variety of non-mechanical signals are necessary to dictate to such transmission when a mechanical ratio change is effected. Obviously, conventional manual transmissions can be considered variable in that with the operation of a clutch to disengage the transmission from a power source and appropriate levers and linkages, one of several gear ratios may be selected.
Transmissions that are truly variable, that is, transmissions that provide an infinite gradation of ratios between input and output shafts over at least a given range of rotational speed, are usually not purely mechanical. Those transmissions that are mechanical and provide this infinite ratio of input/output shaft speed tend to be very inefficient. For example, various friction drives sometimes depend on varying effective diameters of intersecting wheels or cones to effectuate an infinite varying ratio of input to output shaft speed. Refinements in these types of mechanical infinitely variable transmissions frequently limit their torque and horsepower capacities.
Variable transmissions incorporating a fundamental design directed to a particular type of power source may be inapplicable when directed to another. For example, variable transmissions designed for application with internal combustion engines are usually totally inappropriate when the power source is other than an IC engine. For example, electric motors that may be utilized for propelling vehicles generally have excellent torque characteristics and do not require the torque multiplication over the speed range of a typical IC engine. However, to maintain the overall vehicle efficiency it is frequently desirable to provide a variable transmission to maintain peak efficiency operational parameters for the electrical power source and electric motor while giving flexibility to vehicle performance.